Add support for enum types with AbslStringify

PiperOrigin-RevId: 487394692
Change-Id: I55e9b57055483dc921e9773c3643ea9be4f9bdf6

Author: Abseil Team

absl/strings/internal/str_format/arg.h

@@ -18,17 +18,20 @@
 #include <string.h>
 #include <wchar.h>
 
+#include <algorithm>
 #include <cstdio>
 #include <iomanip>
 #include <limits>
 #include <memory>
 #include <sstream>
 #include <string>
 #include <type_traits>
+#include <utility>
 
 #include "absl/base/port.h"
 #include "absl/meta/type_traits.h"
 #include "absl/numeric/int128.h"
+#include "absl/strings/internal/has_absl_stringify.h"
 #include "absl/strings/internal/str_format/extension.h"
 #include "absl/strings/string_view.h"
 
@@ -271,7 +274,8 @@ IntegralConvertResult FormatConvertImpl(T v, FormatConversionSpecImpl conv,
 // FormatArgImpl will use the underlying Convert functions instead.
 template <typename T>
 typename std::enable_if<std::is_enum<T>::value &&
-                            !HasUserDefinedConvert<T>::value,
+                            !HasUserDefinedConvert<T>::value &&
+                            !strings_internal::HasAbslStringify<T>::value,
                         IntegralConvertResult>::type
 FormatConvertImpl(T v, FormatConversionSpecImpl conv, FormatSinkImpl* sink);
 
@@ -384,7 +388,8 @@ class FormatArgImpl {
   template <typename T, typename = void>
   struct DecayType {
     static constexpr bool kHasUserDefined =
-        str_format_internal::HasUserDefinedConvert<T>::value;
+        str_format_internal::HasUserDefinedConvert<T>::value ||
+        strings_internal::HasAbslStringify<T>::value;
     using type = typename std::conditional<
         !kHasUserDefined && std::is_convertible<T, const char*>::value,
         const char*,
@@ -396,6 +401,7 @@ class FormatArgImpl {
   struct DecayType<T,
                    typename std::enable_if<
                        !str_format_internal::HasUserDefinedConvert<T>::value &&
+                       !strings_internal::HasAbslStringify<T>::value &&
                        std::is_enum<T>::value>::type> {
     using type = typename std::underlying_type<T>::type;
   };

absl/strings/str_cat.h

@@ -318,7 +318,8 @@ class AlphaNum {
   // This overload matches only scoped enums.
   template <typename T,
             typename = typename std::enable_if<
-                std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type>
+                std::is_enum<T>{} && !std::is_convertible<T, int>{} &&
+                !strings_internal::HasAbslStringify<T>::value>::type>
   AlphaNum(T e)  // NOLINT(runtime/explicit)
       : AlphaNum(static_cast<typename std::underlying_type<T>::type>(e)) {}
 

absl/strings/str_cat_test.cc

@@ -650,4 +650,16 @@ TEST(StrCat, AbslStringifyExampleUsingFormat) {
   EXPECT_EQ(absl::StrCat("a ", p, " z"), "a (10, 20) z");
 }
 
+enum class EnumWithStringify { Many = 0, Choices = 1 };
+
+template <typename Sink>
+void AbslStringify(Sink& sink, EnumWithStringify e) {
+  absl::Format(&sink, "%s", e == EnumWithStringify::Many ? "Many" : "Choices");
+}
+
+TEST(StrCat, AbslStringifyWithEnum) {
+  const auto e = EnumWithStringify::Choices;
+  EXPECT_EQ(absl::StrCat(e), "Choices");
+}
+
 }  // namespace

absl/strings/str_format_test.cc

@@ -1135,6 +1135,18 @@ TEST_F(FormatExtensionTest, AbslStringifyExampleUsingFormat) {
   EXPECT_EQ(absl::StrFormat("a %v z", p), "a (10, 20) z");
 }
 
+enum class EnumWithStringify { Many = 0, Choices = 1 };
+
+template <typename Sink>
+void AbslStringify(Sink& sink, EnumWithStringify e) {
+  absl::Format(&sink, "%s", e == EnumWithStringify::Many ? "Many" : "Choices");
+}
+
+TEST_F(FormatExtensionTest, AbslStringifyWithEnum) {
+  const auto e = EnumWithStringify::Choices;
+  EXPECT_EQ(absl::StrFormat("My choice is %v", e), "My choice is Choices");
+}
+
 }  // namespace
 
 // Some codegen thunks that we can use to easily dump the generated assembly for